Devices and methods of forming low resistivity noble metal interconnect

ABSTRACT

Devices and methods of fabricating integrated circuit devices for forming low resistivity interconnects are provided. One method includes, for instance: obtaining an intermediate semiconductor interconnect device having a substrate, a cap layer, and a dielectric matrix including a set of trenches and a set of vias; depositing a barrier layer along a top surface of the semiconductor interconnect device; depositing and annealing a metal interconnect material over a top surface of the barrier layer, wherein the metal interconnect material fills the set of trenches and the set of vias; planarizing a top surface of the intermediate semiconductor interconnect device; exposing a portion of the barrier layer between the set of trenches and the set of vias; and depositing a dielectric cap. Also disclosed is an intermediate device formed by the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/168,899, filed 31 May 2016, and entitled “DEVICES ANDMETHODS OF FORMING LOW RESISTIVITY NOBLE METAL INTERCONNECT,” theentirety of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices and methods offabricating semiconductor devices, and more particularly, to devices andmethods of forming low resistivity metal interconnects having noblemetals.

BACKGROUND OF THE INVENTION

For 5 nm and beyond nodes, with the continually increasing demand forsmaller circuit structures and faster device performance, copper lineresistivity begins to climb, decreasing the performance of the nodes.The development of 5 nm nodes and smaller will likely require loweringthe resistivity of the lines in the nodes.

Therefore, it may be desirable to develop methods of fabricating nodeswith lines that have a lower resistivity than copper at such a smallsize.

BRIEF SUMMARY

The shortcomings of the prior art are overcome and additional advantageare provided through the provisions, in one aspect, a method thatincludes, for instance: obtaining an intermediate semiconductorinterconnect device having a substrate, a cap layer, and a dielectricmatrix including a set of trenches and a set of vias; depositing abarrier layer along a top surface of the semiconductor interconnectdevice; depositing a metal interconnect material over a top surface ofthe barrier layer, wherein the metal interconnect material fills the setof trenches and the set of vias; annealing the metal interconnectmaterial; planarizing a top surface of the intermediate semiconductorinterconnect device removing the metal interconnect material above theset of trenches and the set of vias; exposing a portion of the barrierlayer between the set of trenches and the set of vias; and depositing adielectric cap on a set of outer surfaces of the barrier layer and overthe intermediate semiconductor interconnect device.

In another aspect, an intermediate device is provided which includes,for instance: a substrate; a cap layer; a dielectric matrix; a set ofvias extending through the cap layer; a set of trenches extending intothe dielectric matrix, wherein the set of trenches and the set of viasinclude a noble metal; and a dielectric cap.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a method for forming an intermediatesemiconductor interconnect structure, in accordance with one or moreaspects of the present invention;

FIG. 2 depicts a cross-sectional elevation view of one embodiment of anintermediate semiconductor interconnect structure having a substrate, acap layer, and a dielectric matrix including a set of trenches and a setof vias, in accordance with one or more aspects of the presentinvention;

FIG. 3 depicts the structure of FIG. 2 after depositing a barrier layerand a metal interconnect material, in accordance with one or moreaspects of the present invention;

FIG. 4 depicts the structure of FIG. 3 after planarizing a top surfaceof the intermediate semiconductor interconnect structure, in accordancewith one or more aspects of the present invention;

FIG. 5 depicts the structure of FIG. 4 after depositing a sacrificialdielectric cap, in accordance with one or more aspects of the presentinvention;

FIG. 6 depicts the structure of FIG. 5 after depositing a block mask andforming an opening, in accordance with one or more aspects of thepresent invention;

FIG. 7 depicts the structure of FIG. 6 after forming a set of air-gapsand removing the sacrificial dielectric cap and the block mask, inaccordance with one or more aspects of the present invention; and

FIG. 8a depicts the structure of FIG. 7 after oxidizing exposed barrierlayers, in accordance with one or more aspects of the present invention.

FIG. 8b depicts the structure of FIG. 7 after removing exposed barrierlayers, in accordance with one or more aspects of the present invention.

FIG. 9a depicts the structure of FIG. 8a after depositing a dielectriccap around the oxidized exposed barrier layers, in accordance with oneor more aspects of the present invention.

FIG. 9b depicts the structure of FIG. 8b after depositing a dielectriccap following removal of the exposed barrier layers, in accordance withone or more aspects of the present invention;

FIG. 10 depicts a cross-sectional elevation view of one embodiment of anintermediate device having a substrate, a cap layer, a dielectricmatrix, a set of trenches, a set of vias, and a dielectric cap, inaccordance with one or more aspects of the present invention;

FIG. 11 depicts the device of FIG. 10 with a set of air-gaps, inaccordance with one or more aspects of the present invention;

FIG. 12 depicts the device of FIG. 11 with a barrier layer around theset of vias and the set of trenches.

DETAILED DESCRIPTION

Aspects of the present invention and certain features, advantages, anddetails thereof, are explained more fully below with reference to thenon-limiting embodiments illustrated in the accompanying drawings.Descriptions of well-known materials, fabrication tools, processingtechniques, etc., are omitted so as to not unnecessarily obscure theinvention in detail. It should be understood, however, that the detaileddescription and the specific examples, while indicating embodiments ofthe invention, are given by way of illustration only, and are not by wayof limitation. Various substitutions, modifications, additions and/orarrangements within the spirit and/or scope of the underlying inventiveconcepts will be apparent to those skilled in the art from thisdisclosure. Note also that reference is made below to the drawings,which are not drawn to scale for ease of understanding, wherein the samereference numbers used throughout different figures designate the sameor similar components.

Generally stated, disclosed herein are certain integrated circuits,which provide advantages over the above noted, existing semiconductordevices and fabrication processes. Advantageously, the integratedcircuit device fabrication processes disclosed herein provide forsemiconductor devices with a lower line resistivity than previouslypossible using traditional copper lines.

In one aspect, in one embodiment, as shown in FIG. 1, an integratedcircuit device formation process in accordance with one or more aspectsof the present invention may include, for instance: obtaining anintermediate semiconductor interconnect device having a substrate, a caplayer, and a dielectric matrix including a set of trenches and a set ofvias 100; depositing a barrier layer along a top surface of thesemiconductor interconnect device 110; depositing a metal interconnectmaterial over a top surface of the barrier layer 120; annealing themetal interconnect material 130; planarizing a top surface of theintermediate semiconductor interconnect device 140; depositing asacrificial dielectric cap and a block mask over the intermediatesemiconductor interconnect device 150; forming a set of air-gaps andremoving the sacrificial dielectric cap and the block mask 160; anddepositing a dielectric cap on a set of outer surface of the barrierlayer and over the intermediate semiconductor interconnect device 170.

FIGS. 2-8 depict, by way of example only, one detailed embodiment of aportion of a semiconductor device formation process and a portion of anintermediate semiconductor interconnect structure, in accordance withone or more aspects of the present invention. Note that these figuresare not drawn to scale in order to facilitate understanding of theinvention, and that the same reference numerals used throughoutdifferent figures designate the same or similar elements.

FIG. 2 shows a portion of an intermediate semiconductor device generallydenoted 200, depicted at an intermediate semiconductor fabricationstage. The device 200 may have been processed through initial deviceprocessing steps in accordance with the design of the device 200 beingfabricated. For example, the device 200 may include, for instance, asubstrate 210 with a cap layer 220, which may include a dielectricmaterial, disposed on the substrate 210. The substrate 210 may be anysuitable material, for example, silicon. Additionally, dielectric matrix230 may be deposited on substrate 210 or cap layer 220. Dielectricmatrix may include one or more dielectric materials, and may include amixed matrix of materials or a plurality of layers of materials (notshown). Dielectric matrix 230 may include a set of vias 242 and a set oftrenches 244. As illustrated in FIG. 2, the set of vias 242 may extendthrough the cap layer 220 to features below, whilst the set of trenches244 may only extend into the dielectric matrix 230.

In another embodiment (not shown), the substrate of device 200 may be,for example, a silicon on insulator (SOI) substrate (not shown). Forexample, the SOI substrate may include an isolation layer (not shown),which may be a local buried oxide region (BOX) or any suitable materialfor electrically isolating transistors, aligned with the gate structure.In some embodiments, the device is a portion of a back end of line(BEOL) portion of an integrated circuit (IC).

As depicted in FIG. 2, using lithography and etching processes, thedielectric matrix 230 and/or the cap layer 220 may have been etched inthe dielectric matrix 230 to define the set of vias 242 and the set oftrenches 244. The etching may be performed by any suitable etchingprocess, for example, a directional reactive ion etching (RIE).

As depicted in FIG. 3, a barrier layer 250 may be deposited along a topsurface of the device 200 by atomic layer deposition (ALD), chemicalvapor deposition (CVD), physical vapor deposition (PVD), or any othersuitable deposition technique now known or later developed. Forinstance, the barrier layer 250 may have a component of tantalum (Ta),titanium (Ti), or manganese (Mn) and may be less than approximately 3nanometers (nm) thick, and in some embodiments, less than approximately1.5 nm thick. Any deposition capable of forming a consistent thin filmor thin layer of less than 3 nm which can conform to a varied surface,as illustrated in FIG. 3, can be used to deposit the barrier layer 250.

As also depicted in FIG. 3, following deposition of the barrier layer250, a metal interconnect material 260 is deposited over a top surfaceof the barrier layer 250 by ALD or CVD in some embodiments. The metalinterconnect material is deposited, in some embodiments, betweenapproximately 10 nm and approximately 20 nm in thickness, such that itfill the set of vias 242 (FIG. 2) and the set of trenches 244 (FIG. 2).The metal interconnect material 260 can include any noble metal,including but not limited to: ruthenium (Ru), niobium (Nb), rhodium(Rh), iridium (Ir), and platinum (PT). Following deposition of the metalinterconnect material 260, thermal anneal of the material in a range ofapproximately 350° C. to approximately 500° C. can help solidify thematerial. While copper (Cu) has traditionally been the interconnectmaterial of choice, as the line width continues to get smaller fordevice, the resistivity of copper starts to grow. In contrast, noblemetals can have a more desirable resistivity at smaller sizes.

For instance, Ru thin films have a nearly constant resistivity from 20nm to 6 nm, unlike copper, which climbs consistently between 20 nm and 6nm. At approximately 5 nm, Ru can have nearly the same resistivity asCu, and can have a lower resistivity below 5 nm. Additionally, Ru showsno failure due to electromigration (EM), unlike many other interconnectmaterials. The time dependent dielectric breakdown (TDDB) of noble metalthin films can be at least 10 times better than copper. However, as willbe further described below, the resistivity of the metal interconnectmaterial 260 can be lowered even further by increasing the resistance ofthe layer adjacent to the metal interconnect material 260, such asbarrier layer 250. Thus, altering the barrier layer 250 in terms of thecomposition to increase the resistance can lower the resistance of themetal interconnect material 260.

As depicted in FIG. 4, using chemical mechanical polishing, a topsurface of device 200 can be planarized and polished, removing excessmetal interconnect material 260 and providing a smooth surface on whichto continue device fabrication. In one embodiment, following thisplanarizing, barrier layer 250 can be oxidized (not shown) in order tolower the resistance of metal interconnect material 260. Oxidizingbarrier layer 250 can be achieved by annealing the structure in inertambient air, in some instances with less than approximately 1% oxygen,without damaging the metal interconnect material 260. In thisembodiment, the resistance of the metal interconnect material 260 can besignificantly lowered.

As depicted in FIG. 5, a sacrificial dielectric cap 270 can be depositedover device 200. This cap is considered sacrificial as it is used formasking of the underlying structure, and not for functioning of the enddevice.

As depicted in FIG. 6, a block mask 272 can be formed, for example usingstandard lithography and etch techniques, on a top surface ofsacrificial dielectric cap 270, and the sacrificial dielectric cap 270can be removed to expose and form one or more openings over the set oftrenches 244 and the set of vias 242 using any lithography techniques.Following use of the block mask 272, removal via etching techniques maybe performed.

As depicted in FIG. 7, a portion of the barrier layer 250 between atleast some of the set of vias 242 and the set of trenches 244 may beexposed, for instance, by forming a set of air-gaps 280 within thedielectric matrix 230. In some embodiments, regions of the dielectricmatrix 230 may be damaged, for instance, between some or all of the setof trenches 244 and the set of vias 242, for example, to form the set ofair-gaps 280. In some embodiments, H₂ and N₂ plasma is used to damagethe dielectric matrix 230. The damaged material can be removed, forinstance, with diluted hydrofluoric acid, leaving air-gaps 280 betweenat least some of the set of vias 242 and the set of trenches 244. At thesame time, sacrificial dielectric cap 270 and block mask 272 may beremoved with the same material.

As depicted in FIG. 8a , forming air-gaps 280 leaves portions 255 of thebarrier layer 250 exposed, typically the portions covering all or someof the side surfaces of the metal interconnect material 260 that fillsthe set of vias 242 and the set of trenches 244. These portions of thebarrier layer 255 may be oxidized in order to increase theirresistivity, effectively lowering the resistivity of the metalinterconnect material 260. This oxidation may occur by exposure to a wetchemical. In some embodiments, wherein the barrier layer 250 includes ametal component of Ta or Ti, the wet chemical can include hydrogenperoxide (H₂O₂). The metal interconnect material 260 is harder tooxidize, especially at room temperature, so effectively only the exposedbarrier layer 250 oxidizes.

In alternative embodiments, as depicted in FIG. 8b , the exposedportions of barrier layer 250 may be removed rather than oxidized.Removal of the barrier layer 250 allows for the metal interconnectmaterial 260 to interface directly with a dielectric cap 290 (FIG. 9b ),described further below. The dielectric cap 260 will have a higherresistance than barrier layer 250, thus lowering the resistance of metalinterconnect material 260 in the final device. The exposed portions ofthe barrier layer 250 can be removed by exposure to a wet chemical or byetching of any necessary technique.

As depicted in FIG. 9a , a dielectric cap 290 may be deposited on a setof outer surfaces of the barrier layer 250 and over the intermediatesemiconductor interconnect device 200. The dielectric cap 290 canpartially coat the barrier layer 250, but leaving air-gaps 280 (FIG. 7)intact and covered by dielectric cap 290.

As depicted in FIG. 9b , the dielectric cap 290 can coat the exposedmetal interconnect material 260, also leaving air-gaps 280 (FIG. 7)intact. In contrast to FIG. 9a , the material of the dielectric cap,which may include SiN or other dielectric materials, will act as theinterface for metal interconnect material 260. This material can bechosen to have a high resistivity, which will lower the effectiveresistance of metal interconnect material 260 in the end IC.

FIG. 10 depicts an intermediate device 900, which according to someembodiments, includes a substrate 210, a cap layer 220, a dielectricmatrix 230, a set of vias 242 extending through the cap layer 220, a setof trenches 244 extending into the dielectric matrix 230, and adielectric cap 290. In these embodiments, the set of trenches 244 andthe set of vias 242 include a noble metal. The other materials are asdescribed above.

As depicted in FIG. 11, intermediate device 900 can include a set ofair-gaps 280 between at least some of the set of vias 242 and the set oftrenches 244. As can be seen, when air-gaps 280 are present, dielectriccap 290 may line the air-gaps 280.

As depicted in FIG. 12, a barrier layer 250 surrounds the set of vias242 and the set of trenches 244, however the barrier layer 255 in thevicinity of the set of air-gaps 280 (depicted orange in informaldrawings) is an oxidized material of one of the above disclosed barrierlayer materials with the component of Ta or Ti. In some embodiments, theentirety of barrier layer 250 may be oxidized.

It should be appreciated that the novel intermediate semiconductorinterconnect devices and methods of forming the same disclosed abovelower the resistance of BEOL interconnect formations and lines.According to embodiments, surface scatter of the device is reduced byaltering the material of the interconnect itself, and increasing theresistance of the barrier layer decreases the resulting resistance ofthe interconnect material. Noble metals as interconnect materials areadvantageous as the electromigration phenomenon is reduced, in part dueto the higher melting point of the metals. Additionally, noble metalsare more resistant to oxidation, allowing for easier oxidation of thebarrier layers.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of one or more aspects of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand one or more aspects of the invention for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A structure comprising: a dielectric matrix; afirst via extending completely through the dielectric matrix; a secondvia extending completely through the dielectric matrix; a trenchextending partially through the dielectric matrix, the trench arrangedlaterally between the first via and the second via; a first interconnectin the first via; a second interconnect in the second via; a thirdinterconnect in the trench; a barrier layer including a first portionand a second portion lining each of the first via, the second via, andthe trench, a first air-gap arranged laterally between the trench andthe first via; and a second air-gap arranged laterally between thetrench and the second via, wherein the first portion of the barrierlayer is an oxide, the second portion of the barrier layer is a metal,the first air-gap and the second air-gap are fully surrounded byrespective portions of dielectric material, and the first interconnect,the second interconnect, and the third interconnect each comprise anoble metal.
 2. The structure of claim 1, wherein the oxide is tantalumoxide or titanium oxide.
 3. The structure of claim 1, wherein the firstair-gap and the second air-gap are fully located at a depth above adepth of the trench.
 4. The structure of claim 1, wherein the secondportion of the barrier layer is positioned below the first portion ofthe barrier layer in the first via, in the second via, and in thetrench.
 5. The structure of claim 1, wherein the noble metal isruthenium, niobium, rhodium, iridium, or platinum.
 6. The structure ofclaim 1, wherein the first interconnect, the second interconnect, andthe third interconnect have a line width in a range of 6 nm to 20 nm. 7.The structure of claim 6, wherein the noble metal is ruthenium.
 8. Astructure comprising: a dielectric matrix; a first via extendingcompletely through the dielectric matrix; a second via extendingcompletely through the dielectric matrix; a trench extending partiallythrough the dielectric matrix, the trench arranged laterally between thefirst via and the second via; a first interconnect in the first via; asecond interconnect in the second via; a third interconnect in thetrench; a first air-gap arranged laterally between the trench and thefirst via; a second air-gap arranged laterally between the trench andthe second via; and a barrier layer having respective portions liningthe first via, the second via, and the trench, the respective portionsof the barrier layer located in the first via, in the second via, and inthe trench below respective portions of dielectric material wherein therespective portions of dielectric material directly contact the firstinterconnect, the second interconnect, and the third interconnect, thefirst air-gap and the second air-gap are fully surrounded bytherespective portions of dielectric material, and the firstinterconnect, the second interconnect, and the third interconnect eachcomprise a noble metal.
 9. The structure of claim 8, wherein the noblemetal is ruthenium, niobium, rhodium, iridium, or platinum.
 10. Thestructure of claim 8, wherein the first air-gap and the second air-gapare fully located at a depth above a depth of the trench.
 11. Thestructure of claim 8, wherein the first interconnect, the secondinterconnect, and the third interconnect have a line width in a range of6 nm to 20 nm.
 12. The structure of claim 11, wherein the noble metal isruthenium.